This invention relates to a process for the production of 1,4-butanediol from allyl alcohol using a catalyst system comprising a rhodium complex, a ruthenium complex and a diphosphine ligand. The catalyst system is useful in both the hydroformylation step (allyl alcohol to 4-hydroxybutyraldehyde) and the hydrogenation step (4-hydroxybutyraldehyde to 1,4-butanediol). Surprisingly, the catalyst system shows high activity and produces a high ratio of linear:branched (1,4-butanediol:2-methyl-1,3-propanediol) product. The catalyst is also easily recycled with minimal loss of activity.
The production of 1,4-butanediol from allyl alcohol is a well-known and commercially practiced process. See, for example, U.S. Pat. Nos. 4,238,419, 4,678,857, 4,215,177, 5,290,743 and the like. Generally, the process consists of a hydroformylation reaction followed by hydrogenation step. In hydroformylation, allyl alcohol is reacted with a CO/H2 gas mixture using a rhodium-phosphine catalyst system to form 4-hydroxybutyraldehyde. Then, the 4-hydroxybutyraldehyde is separated from the catalyst by water extraction and hydrogenated over a nickel catalyst to form 1,4-butanediol. See U.S. Pat. No. 5,504,261.
The above reaction sequence involves the use of different catalysts and usually different reaction gas mixtures for each of the reactions. For obvious reasons, it would be advantageous to produce 1,4-butanediol from allyl alcohol using only a single catalyst system.
It has been reported, for example, in Kokai No. S52-78809 by Kawahito, et al. that 1,4-butanediol can be produced from allyl alcohol in a one-step reaction system using a rhodium and a trialkyl phosphine catalyst system. However, a disadvantage of the process described in S52-78809 is the relatively low ratio of 1,4-butanediol to 2-methyl-1,3-propanediol which is produced. U.S. Pat. No. 6,127,584 also discloses a one catalyst process using rhodium and a trialkyl phosphine wherein higher ratios of 1,4-butanediol to 2-methyl-1,3-propanediol are produced. However, this process also produces a significant amount of isobutanol by-product, which has little commercial value.
In sum, new processes that would allow the production of 1,4-butanediol using a single catalyst system are needed. Particularly valuable processes would result in high ratios of 1,4-butanediol (BDO) compared to 2-methyl-1,3-propanediol (MPD), without production of isobutanol by-product.
The invention is a process for producing 1,4-butanediol that comprises first reacting allyl alcohol with a mixture of carbon monoxide and hydrogen in the presence of a solvent and a catalyst system to produce 4-hydroxybutyraldehyde. The catalyst system comprises a rhodium complex, a ruthenium complex and a bidentate diphosphine ligand. The 4-hydroxybutyraldehyde is then reacted with hydrogen in the presence of the catalyst system and the solvent to form 1,4-butanediol. The 1,4-butanediol product is optionally separated from the solvent and the catalyst system by water extraction. The solvent and catalyst system are then optionally recycled to the first step. I surprisingly found that using this catalyst system produced high BDO:MPD ratio with no isobutanol by-product.